1. Field of the Invention
This invention relates generally to a master cylinder for a brake or a clutch system of a vehicle and more particularly to such a master cylinder including a molded cylinder of a synthetic resin.
2. Prior Art
Generally, a master cylinder of the type described above comprises a cylinder body of a tubular shape and a pair of mounting flanges formed on an outer peripheral surface of the cylinder body and extending perpendicularly to the axis of the cylinder body, the mounting flanges being adapted to be fixed to a support structure such as a dashboard of an automotive vehicle to mount the master cylinder thereon. A piston is received in the cylinder body for sliding movement therealong. In the case where the cylinder body and the mounting flanges are made of a synthetic resin, they are formed as a one-piece molded construction. The mounting flanges are relatively to provide an increased mechanical strength. Therefore, such thick mounting flanges are subjected to shrinkage, so that the inner peripheral surface of the cylinder body is recessed at a portion corresponding to the connecting portions of the mounting flanges. The piston is not sealingly moved along the internal bore of the cylinder body because of the presence of such a recess. For this reason, conventionally, the piston is adapted to be slidingly moved along that portion of the internal bore other than the recessed portion thereof. As a result, the cylinder body of a synthetic resin is longer than that of metal.
Another known master cylinder as disclosed in U.S. Pat. No. 4,505,112 comprises a cylinder body of a synthetic resin, an outer tubular portion disposed in spaced, concentric relation to the cylinder body and a connecting portion interconnecting the forward end of the tubular portion and the outer peripheral surface of the cylinder body. The piston is movable along the cylinder body between a point disposed rearwardly of the connecting portion and a point adjacent to the rearward end of the cylinder body. With this construction, the length of the cylinder body is reduced by virtue of the provision of the tubular portion. However, the piston is also adapted to be moved along that portion of the internal bore of the cylinder body other than the connecting portion since the internal bore is recessed at a portion corresponding to the connecting portion. This limits the design of the master cylinder, and particularly the mounting flanges can not be spaced away from the connecting portion so much. If so, the strength of the tubular portion is not sufficient to support the mounting flanges.